1. Field of the Invention
The present invention relates generally to a moving blade of a gas turbine used for thermal power generation, etc., and more specifically to a moving blade in which a cooling structure of a shroud is simplified and the cooling performance thereof is enhanced.
2. Description of the Prior Art
FIG. 18 is a view showing a representative moving blade of a gas turbine in the prior art, wherein FIG. 18(a) is a longitudinal cross sectional view thereof and FIG. 18(b) is a cross sectional view taken on line M--M of FIG. 18(a). In the figure, numeral 221 designates a moving blade, numeral 222 designates a shroud at a terminal end thereof and numeral 223 designates a fin provided on the shroud 222. Numeral 224 designates a plurality of holes bored in the moving blade 221, numeral 225 designates a multiplicity of pin fins provided on an inner wall of the moving blade 221 and numeral 226 designates a rib for supporting a cavity 229. Numeral 227 designates a hub portion, numeral 228 designates a blade root portion and numeral 229 designates the cavity as mentioned above.
FIG. 19 is a cross sectional view taken on line N--N of FIG. 18(a) and FIG. 20 is a cross sectional view taken on line P--P of FIG. 19. In FIGS. 19 and 20, there are formed two cavities 230, 231, which are independent of each other, in the shroud 222. The cavities 230, 231 are closed at their interiors by plugs 232, 233, respectively, inserted into upper surface portions thereof, and the holes 224 of the moving blade 221 connect to the cavities 230, 231, respectively, so that cooling air is supplied therethrough into the cavities 230, 231. Also provided in the shroud 222 are a plurality of cooling holes 234 which extend from the cavities 230, 231 to open at mutually opposing side ends of the shroud 222 so that the cooling air flows out therefrom.
In the moving blade constructed as mentioned above, the cooling air flows into the cavity 229 through the blade root portion 228, as shown by arrows in FIG. 18, for cooling of a blade base portion, with the heat transfer rate being enhanced by the pin fins 225, to then be led into a terminal end portion of the blade through the holes 224. The cooling air enters the cavities 230, 231 of the shroud 222 to flow through the cooling holes 234 in mutually opposing directions for cooling of the entire portion of the shroud 222, and then flows out of both of the mutually opposing side ends of the shroud 222.
In the moving blade 221, there is provided the shroud 222 at the terminal end of the moving blade 221, as mentioned above, and the shroud 222 is formed integrally with the moving blade 221. The shroud 222 itself functions to reduce gas leaking through the terminal end of the moving blade 221 and is arranged to form a series of blade groups, wherein mutually adjacent shrouds 222 are jointed together with their end faces being connected by pressing against each other, so that vibration proofing of the moving blade 221 is enhanced. In the moving blade 221, vibrations occur in two directions, of the axial direction and radial direction, but the shroud 222 is made with its end face being formed obliquely, and thereby the vibrations in both directions are suppressed. Also, there is provided the fin 223 to the shroud 222 by cutting, the object of which is to reduce gas leaking through the terminal end of the moving blade 221 and to prevent the shroud 222 from making contact with a casing side component.
As mentioned above, in the prior art gas turbine moving blade, the cooling air flows through the holes 224 of the moving blade 221 to join in the cavities 230, 231 and then flows therefrom through the cooling holes 234 of the shroud 222 in the mutually opposing directions for cooling of the entire portion of the shroud 222 to flow out of both of the mutually opposing side ends of the shroud 222. That is, in terms of the flow of the cooling air in the shroud, there are provided the plurality of cooling holes 234 extending from each of the cavities 230, 231 to both of the side ends of the shroud 222, and there is a difference in the resistance between each of the cooling holes 234, so that the flow rate of the cooling air therein differs corresponding to each of the cooling holes 234. The cooling air thus does not flow uniformly therein and a uniform distribution adjustment of the cooling air is difficult, with the result that a uniform cooling of the shroud is not effected under the present circumstances.